One of the greatest concerns which arises during significant seismic activity or "earthquakes" is that which occurs as the result of natural gas system leakage within homes or other buildings and facilities. In a typical scenario, the violent shaking and structure damage which may occur during a substantial earthquake or its associated preshocks or aftershocks may sever one or more gas lines within the building which in turn opens a discharge leakage through which the pressurized gas freely flows to eventually fill a portion of the building. The escaped gas is, of course, flammable and subject to extremely dangerous explosion once ignited.
Recognizing this extreme danger, safety instructions to individuals in the event of seismic activity routinely includes instructions to endeavor following any quake to detect the odor of natural gas within the building and, if so detected, evacuate the building and close the main gas supply to the building. These instructions are fine for dwellings actively monitored. However, in many instances, escaped gas goes undetected because earthquakes have occurred at times when such dwellings are unoccupied. In addition, persons injured by the building damage or quake itself as well as physically impaired people having handicapped conditions or the like are simply unlikely to be able to conduct an adequate inspection and perform the main supply gas shutoff.
To meet the need for more reliable gas shutoff during dangerous earthquakes, practitioners in the art have provided a variety of gas shutoff valves which are automatic in their shutoff operation once seismic activity above a predetermined magnitude is detected. For example, U.S. Pat. No. 3,783,887 issued to Shoji sets forth a SELF-CLOSING VALVE DEVICE IN A PIPING SYSTEM OF FLUIDS in which a vertically oriented chamber includes an inlet coupling and an outlet coupling. A valve seat is formed at the lower portion of the vertical chamber near the outlet coupling of the gas valve. A magnet in the upper portion of the gas valve chamber magnetically supports an otherwise freely movable steel ball having a size selected to provide closure and obstruction of the valve seat in the event a seismic activity shakes the steel ball loose from its magnetic support. Thus, in the event of seismic activity exceeding a predetermined magnitude, the steel ball is shaken loose from its magnetic support and falls downwardly within the vertical chamber to block the valve seat and provide gas valve closure.
U.S. Pat. No. 4,640,303 issued to Greenberg sets forth a SEISMIC ACTIVATED VALVE having a sphere of magnetic material held above a valve seat by a magnet located at the apex of a dome. The inertia of the sphere causes it to roll along the curvature of the dome to move it vertically away from the magnet and out of axial alignment with it when the valve experiences a horizontal thrust. The structure is intended to avoid response to vertical thrusts and the character of gas flow within the valve.
U.S. Pat. No. 3,521,652 issued to Reeks sets forth an INERTIAOPERATED VALVE having a casting defining a frusto-conical seating a magnet positioned adjacent the apex of the seating and a ball of magnetic material adapted to be held in the frusto-conical seating by the magnet until dislodged by a force of predetermined magnitude. Once dislodged, the ball moves a valve member axially to control fluid flow. U.S. Pat. 4,715,394 issued to O'Donnell, et al. sets forth a GAS SUPPLY SAFETY VALVE FOR EARTHQUAKE PROTECTION sensitive to earthquake accelerations on the X, Y and Z axes. A horizontal chamber includes an inlet port and outlet port disposed on opposite ends of the bottom surface thereof. A ball is restrained by an arcuate groove within the chamber and inbetween the inlet and outlet ports of the valve. During seismic activity, the ball is disturbed from its supporting groove and rolls downwardly across an inclined surface to be seated at the outlet port of the gas valve providing a shutoff action. A movable plunger is secured in alignment with the chamber to provide reset by repositioning the ball in its arcuate groove.
U.S. Pat. No. 4,485,832 issued to Plemmons, et al. sets forth an AUTOMATIC GAS SHUTOFF VALVE having a valve housing defining an inlet conduit, an outlet conduit and a central chamber communicating therebetween. A channel is provided around the interior of the valve above the central chamber. A ball normally rests in the channel and is disturbed therefrom during seismic activity and falls through the chamber to a valve seat blocking the outlet conduit for the valve. A movable plunger is supported beneath the valve seat and is used to restore the ball to its raised condition and open the valve.
U.S. Pat. No. 4,116,209 issued to Greer sets forth a SHOCK ACTUATED SHUTOFF VALVE having a valve housing defining a central chamber in communication with an inlet conduit and an outlet conduit. The housing further includes an enclosed stowage arm located within the central chamber. A valve element is disposed upon the stowage arm and is releasibly supported thereby. Vibratory force affects the displacement of the valve element from the support member permitting it to fall downwardly within the valve housing and block the gas flow through the valve.
U.S. Pat. No. 4,817,657 issued to Kovacs sets forth an INERTIALLY ACTIVATED SHUTOFF VALVE responsive to a jarring force such as an earthquake. The valve includes a valve body defining a tapered chamber in communication with an inlet portion and an outlet port. A taper weighted member is supported at the upper portion of the chamber and is released during jarring forces to fall downwardly within the tapered chamber and provide closure of the inlet and outlet ports thereof. A movable rod is provided to restore the closure element to its raised or open valve condition.
While the foregoing described prior art devices have provided some measure of increase safety for natural gas systems and the like during seismic activity, there remains nonetheless a continuing need in the art for evermore useful and improved gas shutoff valves which reliably function in response to seismic activity.